Scientists have long puzzled over the erratically contoured cells in the outer layers of plants. According to a study published last month in eLife, the complex shapes may emerge to prevent cells from bulging under the internal stress produced by turgor pressure.

Researchers simulated plant cell growth with computer models and found that “paving” leaf surfaces with curvy cells, rather than smooth ones, reduces the stress on epidermal cell walls. They also found that complex puzzle-shape cells develop in parts of the plant that grow isotropically—uniformly in all directions—such as in leaves. In organs that grow directionally, such as roots or stems, cells that are long and thin can reduce stress on the cell walls.